feat(changelog): make remote data available in context

[orhun]

Description

This PR updates the changelog processing order to make remote data (e.g. GitHub commits, pull requests, etc.) available in the context.

Motivation and Context

git cliff --github-repo orhun/git-cliff -c examples/github.toml -x --no-exec -u

This command will now contain the GitHub data such as:

 "github": {
      "contributors": [
        {
          "username": "bukowa",
          "pr_title": "style(lint): fix formatting",
          "pr_number": 702,
          "pr_labels": [],
          "is_first_time": true
        },
    ],
}

Might fix #687

How Has This Been Tested?

Locally.

Types of Changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation (no code change)
• [ ] Refactor (refactoring production code)
• [ ] Other

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [x] I have formatted the code with rustfmt.
• [x] I checked the lints with clippy.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.78378% with 6 lines in your changes missing coverage. Please review.

Project coverage is 37.15%. Comparing base (b7e323f) to head (5368988).

Files	Patch %	Lines
git-cliff-core/src/changelog.rs	83.79%	6 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #703 +/- ## ========================================== + Coverage 36.89% 37.15% +0.27% ========================================== Files 18 18 Lines 1350 1354 +4 ========================================== + Hits 498 503 +5 + Misses 852 851 -1 ``` | [Flag](https://app.codecov.io/gh/orhun/git-cliff/pull/703/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Orhun+Parmaks%C4%B1z) | Coverage Δ | | |---|---|---| | [unit-tests](https://app.codecov.io/gh/orhun/git-cliff/pull/703/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Orhun+Parmaks%C4%B1z) | `37.15% <83.79%> (+0.27%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Orhun+Parmaks%C4%B1z#carryforward-flags-in-the-pull-request-comment) to find out more.

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